Uncontrolled growth of cancer cells is inevitably accompanied by dysregulation of RNA polymerase I activity and ribosome synthesis. Thus, the mechanisms that control ribosomal RNA transcription by RNA polymerase I are directly relevant to the study of cell transformation and tumor cell growth. The overall goal of this project is to characterize the molecular mechanisms that control RNA polymerase I transcription initiation and elongation. Detailed understanding of these regulatory processes will lay the foundation for future therapeutic strategies that target ribosome synthesis to control the growth of cancer cells. Initiation of transcription by RNA polymerase I is regulated in response to growth conditions. However, the mechanisms responsible for this regulation are complex and incompletely defined. Core factor is an essential member of the basal RNA polymerase I transcription machinery but has not been previously identified as a target for regulation of ribosome synthesis. The first aim of this proposal will identify the molecular mechanisms responsible for the regulation core factor activity and abundance. Previous studies directed at characterizing the control of RNA polymerase I transcription have focused almost exclusively on the initiation step of transcription. Recently, it was shown that Spt4p and Spt5p interact with RNA polymerase I and influence transcription elongation and ribosomal RNA processing in vivo. The second aim of this proposal will determine the molecular mechanism(s) by which Spt4p and Spt5p control RNA polymerase I transcription elongation and relate this activity to processing of ribosomal RNA. Recent data demonstrate that processing of ribosomal RNA is coupled to transcription elongation by RNA polymerase I. Additionally, RNA polymerase I elongation was recently identified as a target for regulation of ribosome synthesis rates. However, very few factors that influence transcription elongation by RNA polymerase I have been identified. Thus, there is a need to identify and characterize the factors that control this activity of the enzyme. To address this need, the third aim of this proposal will characterize six candidate transcription elongation factors that were previously identified for their roles in RNA polymerase II transcription and have been shown recently to bind the ribosomal DNA in vivo. PUBLIC HEALTH RELEVANCE: The overall goal of this project is to identify and characterize mechanisms by which eukaryotic cells control ribosomal RNA synthesis and ribosome assembly. Increased ribosome synthesis rates have long been known to correlate with the increased cell proliferation rates observed in cancer cells. These studies will lay the foundation for future therapeutic strategies aimed at controlling cell growth and proliferation.